In the past, PD epidemics erupted sporadically in various locations and years to cause severe losses in vineyards. PD is especially damaging in the southeastern USA where it is endemic and is the primary factor limiting the development of a grape industry based on the high-quality European grapes (Vitis vinifera). PD also is a limiting factor in the production of European grapes in parts of Mexico, Central America, and southwestern USA. Losses to PD may require major replanting where infestations are wide-spread
Strains of Xylella fastidiosa cause economic losses in many other agriculturally important plants, including grapevine, peach, plum, coffee, and citrus. They also cause leaf scorch and declines in many urban shade trees and shrubs, such as elm, oak, oleander, maple, and sycamore. Many strains of Xylella fastidiosa have been discovered, and almost all of these cause leaf scorching of woody perennials such as American elm, maple, mulberry, or plum. Xylella fastidiosa infection of some plants results in slowing of growth or stunting. Some strains of X. fastidiosa have very wide host ranges.
Xylella fastidiosa colonizes the xylem (water conducting elements of plants) and is introduced into plants by insects with piercing/sucking mouthparts that feed on xylem sap. These insects transmit the bacteria from diseased to healthy plants. Plants develop symptoms when the xylem is blocked, thus reducing the flow of water to leaves.
The first evidence of PD infection usually is a drying or “scorching” of leaves. Typically, leaves become slightly yellowed along the margins before drying. In some instances, the outer leaf may dry suddenly while still green. Typically, the leaf dries progressively over a period of days to weeks, leaving a series of concentric zones of discolored and dead tissue.
Currently, the only feasible control for diseases caused by X. fastidiosa is resistance. Virulence to grape of X. fastidiosa strains originally obtained from grapevines with PD varies from avirulent to highly virulent. Weakly virulent strains multiply and move systemically, but more slowly in the plant, producing only minor symptoms. Restriction endonuclease fingerprinting of X. fastidiosa with NotI and SfiI showed a high degree of similarity between the strains from American elder and grapevine.